This invention relates to a midsole for athletic shoes, particularly for medium and long distance running, formed of soft elastic material and having a heel recess containing a firmer elastic material.
Such a midsole is known from U.S. Pat. No. 4,614,046. There a stabilizing element is provided in the shape of a C or L extending in the longitudinal direction of the sole, and the open side of this stabilizing element is provided on the outside of the midsole. By this measure, above all, the twisting of the shin by pivoting of the foot inward, known as "overpronation," i.e., a pronation to a harmful extent, can be counteracted.
Additionally, U.S. Pat. No. 4,490,928 discloses a midsole having a body of resilient foam material and a horseshoe-shaped plate of a rigid synthetic plastic that is recessed into the top surface of the midsole at the heel area. The medial side portion of the horseshoe-shaped plate is longer than the lateral side portion, and at least one leg extends downwardly through the midsole from the medial side portion. The leg serves to resist pronation-causing forces, and the horseshoe-shaped plate serves to distribute them about the heel.
However, there are runners, in whom no pronation, or pronation of less than a harmful extent, occurs and who, when running over longer distances experience, to the contrary, an outward pivoting of the foot, known as "supination". Such motion causes the shin to be twisted outward, which also has a harmful effect on the knee joint.
Thus, the primary object of the invention is to improve a midsole for athletic shoes of the type initially mentioned so that harmful supination positions are avoided, and as flat a position of the foot as possible can be attained quickly. At the same time, it is also sought to assure that the runner does not go from a permissible, reduced supination position to an undesirable, harmful pronation position.
This is achieved by the fact that the stabilizing element consists of a U-shaped part, covering the entire heel edge area, and a part which closes the U-shaped part at the middle part of the foot in a manner creating a window into which an island of the full thickness of the midsole engages. The stabilizing element also has a strip which extends along the lateral side of the midsole up to at least, approximately, the little toe area of a shoe provided with such a midsole.
With the invention, in the entire lateral area of the midsole a high positioning force acting in the direction of the flat position of the foot is achieved. At the same time, by the arrangement of the stabilizing element, an overtilting in a medial direction (pivoting of the foot onto the inner heel edge area) with a subsequent harmful pronation, is avoided by holding the pivoting angle of the foot to a minimum.
These and further objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, a single embodiment in accordance with the present invention.